Method of making a recess termination in a component

ABSTRACT

In a method of making a recess termination in a component, the recess (2) extending with its tip (4) from the surface (3) of a wall (1) of the component into the interior of the wall (1), the tip (4) of the recess (2) is deflected in its direction by at least about 180° relative to the main extension direction of the recess (2), the deflection being effected in a curvature (6) which is generously dimensioned from the point of view of notch and fracture mechanics, the maximum radius (4) of curvature being placed at the point of maximum stress in the wall (1), the tip (4) of the recess (2) ending in an at least largely relieved region, and the wall piece in the interior of the arc (6) of curvature remaining connected to the rest of the wall (1) via an adequately dimensioned material bridge (5).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of making a recess termination in acomponent. In this case, the termination of the recess is to be designedin such a way that the latter does not continue to grow despite loadingof the component.

2. Discussion of Background

In the construction of machines and apparatus there is often the problemof preventing further growth of a crack which has grown on account ofexcessive loading or of eliminating crack growth due to the notch effectat the end of a relief slot specifically made in a wall of a component.A known method of the prior art for solving this problem consists in"boring out" the recess, by a hole of sufficiently large bore diameterbeing drilled at the tip of the crack or slot.

The term recess is intended to refer below to a crack which has grownnaturally, to a weakening, crack-directing notch as "predeterminedbreaking point" which permits crack propagation only in the prescribeddirection and causes only a minimum leakage cross section on account ofthe small opening of a crack which has grown in the remaining wallthickness, or to a slot specifically made in a component.

A considerable leakage cross section, which is undesirable, for example,in fluid-flow machine construction, is disadvantageously produced by theboring out of the recess tip. For this reason and for strength reasons,a bore diameter which is too small to result in a lasting solution tothe abovementioned problem is therefore often selected in practice.

On the basis of knowledge gained in the field of fracture mechanics, itis known that, by a suitable run-out of the crack tip, i.e. a suitableconfiguration of the recess termination, further growth of the crack orthe recess can be inhibited or prevented, so that it is possible tocontinue to use and load the component.

SUMMARY OF THE INVENTION

Accordingly, in attempting to avoid the abovementioned disadvantages ofthe prior art, one object of the invention is to provide a novel methodof making a recess termination in a component, with which method, on theone hand, crack development or further crack growth in the recess isreliably prevented and, on the other hand, no increased leakage occurs.

According to the invention, this is achieved in that, in a method ofmaking a recess termination in a component, the tip of the recess isdeflected in its direction by at least about 180° relative to the mainextension direction of the recess, the deflection being effected in acurvature which is generously dimensioned from the point of view ofnotch and fracture mechanics, the maximum radius of curvature beingplaced at the point of maximum stress in the wall, and the wall piece inthe interior of the arc of curvature remaining connected to the rest ofthe wall via an adequately dimensioned material bridge.

The advantages of the invention consist in the fact that the furthergrowth of an existing crack is prevented or the start of a crack at theend of a slot which is made deliberately is ruled out, so that thecomponent can continue to be stressed without problem. In addition, nolarge holes are produced in the component by the method according to theinvention, so that leakage losses, for example in thermal fluid-flowmachines, can be minimized.

It is especially expedient if the curvature is designed in the form of asemicircle up to a three-quarter circle, an ellipse or spiral or similarcurve. These forms are especially well suited to prevent an incipientcrack or to stop the crack growth.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a section through a recess in a first embodiment variant ofthe invention;

FIG. 2 shows a section through a recess in a second embodiment variantof the invention;

FIG. 3 shows a section through a recess in a third embodiment variant ofthe invention;

FIG. 4 shows a section through a recess in a fourth embodiment variantof the invention;

FIG. 5 shows a section through a recess in a fifth embodiment variant ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, FIG. 1shows a section through a recess 2 made specifically in a wall 1. Thisrecess 2 is, for example, a relief slot which has been made in the wall1 by means of suitable manufacturing processes (e.g. electricaldischarge machining). The recess 2 extends from the side edge 3 into theinterior of the wall 1 and has a width from typically 3 mm upward.

According to the invention, the termination of the relief slot is nowmade in such a way that the tip 4 of the recess 2 is deflected in itsdirection by about 180° relative to the main extension direction of therecess 2, so that the termination of the relief slot 2 is made in thewall 1 in the form of a semicircle having the radius r of curvature. Thesize of the radius r of the curvature 6 is determined from the point ofview of notch and fracture mechanics and is generously dimensioned inorder to ensure that an incipient crack or even crack growth does nottake place anywhere. In this case, the tip 4 of the relief slot 2 ismade in a largely relieved region and positioned there, i.e. it ends inthis region.

The configuration of the termination in the individual case depends inthe first place on the magnitude of the stresses and in the second placeon their direction. In addition, the available space and questions ofoptimization--greatest possible security against incipient cracks at thesmallest possible leakage--are important. A further important aspect ishow precisely the magnitude and direction of the loading under all theoperating conditions which occur are known or can be calculated inadvance.

FIG. 1 shows a more simple form for a case in which stress magnitude anddirection are well known.

Further forms of terminations, which may be of advantage in specialcases, are shown by way of example in FIG. 2 to FIG. 5.

FIG. 2, in contrast to FIG. 1, shows how the tip 4 of the slot 2 isdeflected in its direction by more than 180° relative to the mainextension direction of the slot 2. In the example, the termination ofthe recess 2 is designed in the form of a three-quarter circle, andhere, too, the tip 4 runs into a largely or completely relieved regionand ends there.

Here, as well as in the following examples, the wall piece in theinterior of the end arc still remains connected to the rest of the wallvia an adequately dimensioned material bridge 5.

FIGS. 3 and 4 show embodiment variants in which the recess terminationis designed in the form of a semi-ellipse up to a three-quarter ellipseor a similar curve. Here, the maximum radius r of curvature is in eachcase placed at the point of maximum stress in the wall, so that theellipses are accordingly designed to differ in the extent of their widthand height. FIG. 3 also shows that the recess 2 need not necessarilyextend perpendicularly from the side edge 3 of the wall 1.

Finally, FIG. 5 shows a sectional representation of a recess 2 in a wall1 in which the recess termination is designed in the form of a spiral.Such a termination provides the greatest possible resistance againstcrack growth if loading directions which vary at random are to beexpected. All the other features of the invention are included asalready described above.

The invention is of course not restricted to the exemplary embodimentsjust described. For example, the recess 2 may be a weakening,crack-directing notch which is deliberately made in the wall, is of adepth of less than the local wall thickness, and ensures that a crackforms only in the prescribed form and propagates with the advantage of aminimum leakage cross section of the crack, which has grown in theremaining wall thickness.

In addition, the recess 2 may, for example, also be a crack which hasdeveloped unintentionally as a result of excessive loading or as aresult of material defects in the wall 1. In order to prevent furthergrowth of this crack and thus to enable the wall 1 or the component tobe stressed for an even longer period, a termination in the form shownabove may be made subsequently by suitable manufacturing processes.Alternatively, the termination may be made on the surface as acrack-directing notch, or the crack growth could also be specificallyinfluenced in such a way that the propagation direction of the crack ischanged by the selection of suitable stress conditions, so that thecrack tip, in relation to the main propagation direction, is turned backby at least about 180° in such a way that a curvature in the form of asemicircle or a three-quarter circle or an ellipse or spiral is obtainedas crack termination. In this case, the maximum radius r of curvature,as already described above, should be realized at the point of maximumstress, and the crack tip is made in the wall in such a way that it runsinto a largely or completely relieved region, the wall piece in theinterior of the end arc remaining connected to the rest of the wall viaan adequately dimensioned material bridge.

Obviously, numerous modification and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by letters patent ofthe United States is:
 1. A method of making a recess termination in acomponent comprising the steps of:performing a manufacturing process tomake a recess extend to a tip from a side edge of a wall of thecomponent into an interior of the wall, wherein the tip of the recess isdeflected by at least about 180° relative to a main extension directionof the recess and the deflection being effected by a curvature of therecess, a maximum radius (r) of the curvature being placed at a point ofmaximum stress in the wall, the tip of the recess being made in an atleast largely relieved region, and a wall piece in the interior of thecurvature remaining connected to the rest of the wall via an adequatelydimensioned material bridge.
 2. The method as claimed in claim 1,wherein the curvature of the recess is designed in the form of asemicircle up to a three-quarter circle.
 3. The method as claimed inclaim 1, wherein the curvature of the recess is designed in the form ofa semi-ellipse up to a three-quarter ellipse.
 4. The method as claimedin claim 1, wherein the curvature of the recess is designed in the formof a spiral.